1. Field of the Invention
The invention relates to a method of fabricating a semiconductor device, and more particularly to a method of fabricating a semiconductor device in which a wire is to be formed above a via-hole.
2. Description of the Related Art
One of conventional methods of fabricating a semiconductor device is explained hereinbelow with reference to FIGS. 1A to 1E.
As illustrated in FIG. 1A, there are formed device isolation regions 3 at a surface of a semiconductor substrate 1, and diffusion layers 2 adjacent to the device isolation regions 3. A gate oxide film 21 is formed at a surface of the semiconductor substrate 1 between the diffusion layers 2. There is formed a gate electrode 22 on the gate oxide film 21. The gate electrode 22 and the gate oxide film 21 are covered at their side surfaces with sidewalls 23.
Then, a resultant is covered with a first interlayer insulating film 4. Then, there are formed contact holes 5 by photolithography and etching. The contact holes 5 pass through the first interlayer insulating film 4 and reach the diffusion layers 2. Then, there is formed a barrier metal film 12 on an inner surface of the contact holes 5. The barrier metal film is constituted of an about 30 nm-thick titanium film and an about 100 nm-thick titanium nitride film. Then, a resultant is covered with a tungsten film 13 by chemical vapor deposition (CVD) employing WF.sub.6 and H.sub.2 gases as source gases. Then, the tungsten film 13 is etched back to thereby fill the contact holes 5 with tungsten 13.
Then, a first wiring layer 6 is formed over a resultant by sputtering, and subsequently patterned in a desired pattern by photolithography and reactive ion etching. Before or while the above mentioned steps are carried out, the semiconductor substrate 1 is processed to have a desired impurity profile therein by ion implantation and annealing and all that.
Then, as illustrated in FIG. 1B, a hydrogenated amorphous carbon film 7 is formed by about 0.1 .mu.m over a resultant, and a fluorinated amorphous carbon film 8 is formed by about 1.0 .mu.m over the hydrogenated amorphous carbon film 7.
Then, as illustrated in FIG. 1C, photoresist 9 is formed by about 1.0 .mu.m over the fluorinated amorphous carbon film 8. Then, the photoresist 9 is exposed to light at a portion where via-holes 10 are to be formed, and developed to thereby remove the portion of the photoresist 9. With the photoresist 9 being partially removed, reactive ion etching (RIE) is carried out to thereby etch the fluorinated amorphous carbon 8 and the hydrogenated amorphous carbon 7. As a result, there are formed via-holes 10. Since the photoresist 9 is exposed to plasma during the reactive ion etching, there is formed a cured layer 11 at the top of the photoresist 9, as illustrated in FIG. 1C.
Then, the cured layer 11 formed on the photoresist 9 is exposed to plasma in oxygen atmosphere to thereby remove the cured layer 11. Thereafter, the photoresist 9 is removed by organic release solution, as illustrated in FIG. 1D.
Then, as illustrated in FIG. 1E, a barrier metal film 32 is formed on an inner surface of the via-holes 10. The barrier metal film 32 consists of an about 30 nm-thick titanium film and an about 100 nm-thick titanium nitride film. Then, a tungsten film 33 is deposited over a resultant by CVD employing WF.sub.6 and H.sub.2 gases as source gases. Thereafter, the tungsten film 33 is etched back to thereby fill the via-hole 10 with tungsten 33. Then, an aluminum layer 14 is deposited over a resultant by sputtering, and thereafter is patterned, as illustrated in FIG. 1E.
In the above mentioned conventional method, when the cured layer 11 formed on the photoresist 9 by reactive ion etching is removed by plasma in oxygen atmosphere, an inner wall of the via-hole 10 is also etched, as illustrated in FIG. 1D, thereby posing a problem that the via-holes 10 have a greater side length than a designed side length.
With respect to photoresist removal, processing variables such as photoresist type are discussed in "A Plasma Oxidation Process for Removing Photoresist Films", Stephen M. Irving, Solid State Technology, June 1971, pp. 47-51.